1. Field of the Invention
The present invention relates to a semiconductor laser apparatus and a method of observing a light emitting portion of the semiconductor laser apparatus and, in particular, to a structure of electrodes of a semiconductor laser chip. The present invention is preferably used for the semiconductor laser apparatus utilized for an optical communication device, an optical information reproducing unit and the like and the method of observing the light emitting portion of the semiconductor laser apparatus.
2. Related Background Art
A configuration of a conventional semiconductor laser apparatus is shown in FIG. 8 and FIG. 9. In FIG. 8 and FIG. 9, reference numeral 1 denotes an electrode of an Au wire bonding surface, reference numeral 2 denotes an electrode on the side of a base for a stem, a photodiode and the like, reference numeral 3 denotes a laser diode crystal (laser diode chip), reference numerals 4, 5 denote an anode surface and a cathode surface of the laser diode chip 3, reference numeral 6 denotes a base for stem or a photo diode of a package and the like, reference numeral 7 denotes a light emitting (resonator) portion inside the laser diode chip, reference numeral 8 denotes an AU bonding wire and reference numeral 9 denotes an end surface for emitting a laser beam.
The laser diode chip 3 has the electrode formed on the entireties of the anode surface and the cathode surface 4, 5 and either of the surfaces is connected to the base 6 such as the package stem or the photo diode and the like and, to the other surface, the Au wire 8 is connected so as to make an electrical contact to the outside.
Connecting a power source between the Au wire of the laser diode chip and the package stem or the photo diode as configured above and letting an electric current flow to the laser diode chip 3 excite a laser oscillation at the light emitting (resonator) portion 7 and a laser beam can be obtained from the end surface 9.
It is generally known that in the semiconductor laser apparatus, external electrical stresses such as static electricity or surges cause crystal breakage in the light emitting (resonator) portion of the laser diode chip, and through life deterioration where the light emitting output is lowered according to the applying time of the current to the laser diode chip, crystal trouble develops in the light emitting (resonator) portion.
When the breakage or the trouble develops as above in the light emitting (resonator) portion 7 of the laser diode chip and the light emitting output is lowered, a direct observation of the light emitting (resonator) portion inside the laser diode chip is the effective means by which the cause of the lowering of the light emitting output is studied. However, in case of the above described conventional example as shown in FIG. 8, because the electrode 1 of the laser diode chip is disposed approximately on the whole of the laser diode chip anode surface 4 and also the electrode 2 is similarly formed on the whole of the cathode surface 5 and, moreover, the one side thereof (here, the cathode surface)is fixed to the base of the stem, it was impossible to observe a state of the light emitting (resonator) portion 7 inside the laser diode chip from the upper or the lower direction of the laser diode chip by using an optical microscope or an electron microscope.
In fact, when the observation of the internal light emitting (resonator) portion is to be performed, according to the conventional technology, the emission status can be observed only after the electrode materials are removed by chemical agent and the anode surface or the cathode surface of the laser diode chip is exposed, and then the electrode is formed again in the position where no interference is caused with the observation of the light emitting (resonator) portion and the electrical contact is made.
Therefore, the applicant of the present invention has already filed an application for the structure for observing the light emitting portion inside the laser diode chip by disposing an opening in the electrode 1 (Japanese Patent Application Laid-Open No. 11-274566).
However, it is not always necessary to observe the light emitting portion in a normal using state. Moreover, there are some cases where the light emitting portion 9 in FIG. 8, for example, is separated from the electrode 1 and it is better to observe it from the electrode 2 side. It is, therefore, desirable that when breakage or trouble develops in the light emitting (resonator) portion of the laser diode chip and the light emitting output is lowered, the above-described opening is disposed, as occasion demands, from the base 6 side such as a package or the like so that the internal light emitting portion of the laser diode chip can be observed.